Wireless communication has been used as a technology for eliminating burdens of cabling work in traditional wired communication and for realizing mobile communication. For example, wireless LANs (local area networks) using standards, such as an IEEE (The Institute of Electrical and Electronics Engineers) 802.11 standard, have already been widely used. In recent years, broadband Internet connection services using wireless LANs typified by HotSpot (registered trademark) have become popular. That is, base stations and access points are installed at cafes, hotels, fast food restaurants, stations, airports and so on to offer service areas where the Internet is available.
With such wireless communication services, users can enjoy services, such as IP (internet protocol) phone and access to a WWW (World Wide Web) information domain, even while on the go. That is, at various places, a client terminal can perform transfer or synchronization processing on data to be used, through connection to a server via a nearest base station or access point. Thus, more and more information devices that function as client terminals are equipped with wireless LAN (local area network) capabilities.
In recent years, outdoor wireless LAN services are also spreading rapidly. The number of access points installed at public places is increasing, and the service areas are expanding continuously. However, the service areas have not covered all places yet, and thus, for example, the client terminal may fall into an offline state in which it is not connectable to any base station or access point, while the client terminal is in transit. While offline, the client terminal is unable to perform information transfer or synchronization processing with the server.
When the information transfer or synchronization processing between the client terminal and the server is performed by a manual operation of the user before the client terminal goes offline, the user can use the latest information even with the client terminal being offline. However, the user performing the manual operation each time the client terminal goes offline is cumbersome and is not practical.
Alternatively, when the information transfer or synchronization processing between the client terminal and the server is periodically performed, the user does not have to perform the cumbersome manual operation. However, since the transfer or synchronization processing of data to be used is not necessarily always performed before the client terminal goes offline, there may be cases in which, when the client terminal goes offline, the user cannot perform processing, such as reference, edit, and deletion, on the data to be used.
When the information to be used is stored in the client terminal so as to be usable while offline, highly confidential information such as data related to personal information can be leaked when the client terminal falls into the hands of a third party or is left unoperated for a long time. This leads to a problem of decreased security.
For example, a mobile-phone total management system in which personal information, such as phone numbers and email addresses, are stored in a server protected with robust security rather than being held in mobile phones is available (e.g., refer to “http://houjin.kcs.ne.jp/solution/secure_top.html”, available as of Jul. 23, 2009). With the system, a telephone directory can be used with a mobile phone upon connection to the server. In addition, even if the mobile phone is lost or stolen, the precious data is safely protected. Also, the system allows an application for a telephone directory to be downloaded for offline use and also has a function of forcibly deleting the downloaded telephone directory through remote operation and a function of automatically deleting the telephone directory on the basis of an authentication failure count. However, in order to use the telephone directory with the mobile phone being offline, the user has to download the telephone-directory application before the mobile phone goes offline. Also, since the downloaded telephone-directory application is kept stored in the mobile phone, the security declines compared to a case in which the telephone directory is stored in only the server. Use of the downloaded telephone-directory application only when the client terminal is offline involves downloading the telephone-directory application before the terminal goes offline and then deleting the downloaded telephone-directory application when the terminal goes online again, which is a cumbersome manual operation for the user.
A scheme in which synchronization processing is executed each time changes are made to data on the server or the client terminal and a scheme in which a request as to whether or not synchronization is to be performed is issued to the server manually, periodically, or each time the client terminal logs in are available, such as those used in Google Sync, Mobile Me, My Phone, and so on. In those schemes, however, since the communication state of the client terminal and the synchronization timing are not correlated with each other, information to be used may not generally be synchronized before the client terminal goes offline.
Japanese Unexamined Patent Application Publication No. 2004-94577 discloses an information terminal device that issues, when the strength of radio waves for communication decreases during synchronization processing, an alarm to a user so that the synchronization processing is not interrupted.
Japanese Unexamined Patent Application Publication No. 2003-309791 discloses a storage device that can record data, received over radio waves, to a recording medium and allows data loss and partial-data recording to be prevented when the radio-wave state deteriorates, by suspending an operation for writing data to the recording medium or generating an alarm sound for the user.
Japanese Unexamined Patent Application Publication No. 2000-155710 discloses a synchronization processing method in which, when a server and a local storage device are performing synchronization with each other, the synchronization processing is executed for each resource in accordance with a schedule specifying date and time and the day of a week when the synchronization processing for each resource is to be executed.
Japanese Unexamined Patent Application Publication No. 2007-96746 discloses a terminal equipped with a mobile-phone function. For use of a telephone directory, the terminal downloads information of a personal telephone directory from an authentication server.
Japanese Unexamined Patent Application Publication No. 2007-81517 discloses an information storage method. In the method, a mobile communication device stores, in its memory, only an information identifier ID and information recognized by the owner of the mobile communication device. Those pieces of information are managed in an information management server through matching with corresponding information in the information management server. The method, however, has a shortcoming in that the information may not generally be checked when the client terminal goes offline.